A novel apparatus and method for attaching a rounded member, such as an inflator assembly for an automobile air bag, to another member or surface, particularly a flat surface, is disclosed. A spacer, which may take the form of a split ring, is positioned around an attachment surface of the rounded member. Then, while the spacer is supported against further motion along the inflator, a flange having a shank with a tapered inside diameter may be passed around the inflator and spacer. As the inside diameter of the flange narrows to contact the spacer, the flange exerts inward pressure tending to frictionally engage the inflator with the spacer, and the spacer with the flange. Thus, an interference fit having a high retention strength may be comparatively easily and rapidly formed. The spacer may be hardened so as to indent the inflator and/or the flange to enhance the retention strength of the assembly. The spacer may be reconfigured in a number of ways to provide the appropriate combination of resistance against axial pressure and torsion.